Saadaldeen Ali Salim Talib, trade minister of the Arabian Peninsula nation, formally handed over Yemen's entry treaty in a ceremony with WTO chief Roberto Azevedo.
"We have easy access to three continents, Africa, Asia and Europe. Our location is on the highway of trade. Our port in Aden is three hours away from the highway," Talib told reporters.
"We want to be on the value chain with the rest of the economies of the world," he added, saying it would revive an age-old trading history that saw Yemeni seafarer communities take root in places as far apart as Wales and Indonesia.
Existing members had given a green light at a WTO summit in Bali last December, but Yemen then had to ratify its entry deal.
WTO accession negotiations can be tortuous -- Yemen's began in 2000 -- as would-be members first strike deals with countries already in the trade body.
Those accords are then folded together into a single accession treaty setting out the give and take involved in joining the club.
"It's been a hard process," said Talib, underlining that Yemen was also trying to break with years of instability, enacting political and economic reforms hand in hand.
WTO membership is seen as a key step in the global economy because it gives countries easier access to other countries' markets under a set of agreed rules, as well as a forum to deal with trade disputes.
It is also considered a badge of confidence.
"The reform process has not always been easy. But in becoming a member of the WTO, Yemen has sent a very clear signal to traders and investors that the country is open for business," Azevedo told reporters.